Quenched and tempered (Q&T) medium-C steels with various V and Mo additions were studied to understand the relationship between alloy carbide precipitation and hydrogen absorption and trapping behaviours. Heat treatments were selected in the temperature range favourable for V carbide formation, 500-600 °C, leading to higher hardness compared to similar V- and Mo-free alloys due to precipitation hardening. Heat-treated coupons were electrochemically charged to introduce hydrogen, and the bulk hydrogen concentration was measured using melt extraction analysis. Hardness and dislocation density were measured for each tempered condition to relate these properties to the hydrogen absorption and trapping behaviours of each material. Results indicate that dislocation density as well as V and Mo carbide precipitation increase the extent of hydrogen absorbed during charging and the amount of hydrogen remaining trapped after holding at ambient temperature for up to 168 h (1 week).

The influence of microstructure on hydrogen embrittlement of high strength steels for fastener applications is explored in this study. Space limiting applications in areas such as the automotive or agricultural industries provide a need for higher strength fasteners. Albeit, hydrogen embrittlement susceptibility typically increases with strength. Using a 9260 steel alloy, the influence of retained austenite volume fraction in a martensitic matrix was evaluated with microstructures generated via quenching and partitioning. X-ray diffraction and scanning electron microscopy were used to assess the influence of retained austenite in the matrix with different quenching parameters. The quench temperatures varied from 160 °C up to 220 °C, and a constant partitioning temperature of 290 °C was employed for all quench and partitioned conditions. The target hardness for all testing conditions was 52-54 HRC. Slow strain rate tensile testing was conducted with cathodic hydrogen pre-charging that introduced a hydrogen concentration of 1.0-1.5 ppm to evaluate hydrogen embrittlement susceptibility of these various microstructures. The retained austenite volume fraction and carbon content varied with the initial quench temperature. Additionally, the lowest initial quench temperature employed, which had the highest austenite carbon content, had the greatest hydrogen embrittlement resistance for a hydrogen concentration level of 1.0-1.5 ppm.

This paper discuss recent developments in mesh belt heat treating systems used in the production of automotive fasteners. Methods for heat treating threaded fasteners have evolved significantly over the last 20 years as low-capacity shaker hearth, rotary hearth, and plate-belt systems are replaced by soft handling mesh belt heat treatment systems. Design innovations for improving the accuracy of tempering furnace tolerance bands and integrating inline zinc phosphate removal systems are discussed along with their respective benefits.

This paper discusses the basic principles of multi-frequency eddy current testing and explains how it can be used on high-volume production lines to detect faulty heat-treated parts based on case depth, hardness patterns, tensile strength, carbon content, soft spots, and surface decarburization. It also presents examples showing how the method is used in high-speed inspection of cam shafts, screws, balls of various sizes and materials, distance pins, and complex bolts.

Austempering is an alternative hardening process that has been operating under the radar of manufacturers and designers for decades, primarily because its application is directed to fasteners having a cross-section of 12.7 mm or less. The primary goal of austempering is to create an extremely tough microstructure throughout the part’s mass or cross-section, a typical requirement for fasteners. This paper provides an overview of austempering processes and applications.

This study examines the formation and consequences of delta ferrite (Fe₃P) in heat-treated bolts made from SAE10B30 microalloyed steel. The research demonstrates that when phosphated steel undergoes quenching and tempering in neutral or reducing atmospheres without proper cleaning, residual phosphate coating leads to the formation of delta ferrite—a brittle tetragonal phase with high hardness (approximately 450 HV) but poor toughness. Through comparative analysis of phosphate-treated and phosphate-free specimens heat-treated to 43-44 HRC, the authors identify that delta ferrite promotes micro-crack nucleation at grain boundaries, significantly reducing impact resistance, toughness, and fatigue life. The study confirms that proper alkaline cleaning to remove phosphate coatings before heat treatment is essential for preventing delta ferrite formation and maintaining the structural integrity of high-strength bolts (strength class 12.9), particularly those operating under fatigue conditions.

Traditional methods for large stud removal or tightening, such as hydraulic bolt tensioners and induction heaters, are cumbersome, require significant space and specialized power, and often cause damage to fasteners. This paper introduces a patented electric resistance bolting system for stud disassembly and tightening. The system is lightweight, easily transportable by hand, and utilizes readily available power sources, eliminating the need for extensive setup. Capable of simultaneously heating up to six studs, the new technology significantly reduces the time and cost associated with these operations compared to conventional techniques.